The present invention is directed generally to spark plugs, and more particularly to a spark plug employing matching opposing convex surfaces as the spark plug gap.
Prior spark plugs typically provide gap electrodes that are flat and parallel or round and symmetrical (i.e., circular convex to circular concave). One such spark plug provides one or more prongs disposed over the tip of a center or sparking electrode. Such spark plugs generate a spark at the outermost tip of the center electrode which results in the gradual build-up of carbon on the tips of the central electrode and the prongs. The carbon build-up leads to a reduced capacity or failure in generating a spark for igniting the fuel/air mixture in an internal combustion engine. Further, the prongs tend to need re-gapping because of electrical use wear and any unwanted bending of the prongs which can occur during periodic cleaning of the spark plug electrodes.
In order to lengthen operational life, another type of spark plug has a disk-like terminal head concentrically located in spaced relation within a cylindrical ground electrode to provide an annular sparking gap between the ground electrode and the entire circumference of the disk-like terminal head of the sparking electrode. Thus, in this type of spark plug, firing may occur across the annular sparking gap anywhere along its circumferential length and therefore less fouling will occur as compared with spark plugs having a single point-to-point contact between a central electrode and a ground electrode prong. A drawback with spark plugs with annular sparking gaps, however, is that the center electrode and insulator are typically not exposed to enough of the fuel/air mixture to prevent fouling and are susceptible to damage resulting from, for example, accidental dropping of the spark plug. Further, the insulator member of such spark plugs typically does not have enough exposure to the fuel/air mixture for allowing sufficient cooling to prevent an associated insulator heat build-up which can in turn lead to cracking or insulator resistance breakdown.
In view of the foregoing, it is a general object of the present invention to provide a spark plug which overcomes the above-mentioned drawbacks associated with the use and operational life of prior art spark plugs.
In a first aspect of the present invention, a spark plug includes an elongated electrical insulator body defining a first bore extending longitudinally along a central axis of the body from a connector end to a firing end. A sparking electrode communicates with the first bore. The sparking electrode includes a firing tip defining a convex outer surface generally having a radius of curvature. The firing tip has an outermost point generally coinciding with the central axis. A ground electrode includes a sleeve having a support portion adjacent to the firing tip of the sparking electrode. The sleeve defines a second bore accommodating at least a longitudinal end portion of the insulator body adjacent to its firing end. The ground electrode further includes a toroidal member having a convex outer surface. The toroidal member is supported by and spaced from the support portion of the sleeve. The toroidal member forms an annular curve disposed generally in a plane transverse to and having a radial center coinciding with the central axis of the insulator body, whereby each differential segment of the toroidal member radially thereabout is generally equidistant to the firing tip. The toroidal member is a closest portion of the ground electrode relative to the firing tip. At least a portion of the outer surface of the toroidal member opposing the firing tip has a radius of curvature of about that of the firing tip for providing a spark along a path of least resistance from the firing tip of the sparking electrode to a point of contact on the opposing surface defined by the toroidal member of the ground electrode.
In a second aspect of the present invention, a spark plug includes an elongated electrical insulator body defining a first bore extending longitudinally along a central axis of the body from a connector end to a firing end. A sparking electrode communicates with the first bore. The sparking electrode includes a firing tip defining a convex outer surface facing generally away from the connector end and generally has a radius of curvature. The firing tip has an outermost point generally coinciding with the central axis;. A ground electrode includes a sleeve having a support portion adjacent to the firing tip of the sparking electrode. The sleeve defines a second bore accommodating at least a longitudinal end portion of the insulator body adjacent to its firing end. The ground electrode further includes a toroidal member having a convex outer surface. The toroidal member is supported by and spaced from the support portion of the sleeve such that the toroidal member is disposed slightly longitudinally outwardly from the firing tip. The toroidal member forms an annular curve disposed generally in a plane transverse to and having a radial center coinciding with the central axis of the insulator body, whereby each differential segment of the toroidal member radially thereabout is generally equidistant to the firing tip. The toroidal member is a closest portion of the ground electrode relative to the firing tip. At least a portion of the outer surface of the toroidal member opposing the firing tip has a radius of curvature of about that of the firing tip for providing a spark along a path of least resistance from the firing tip of the sparking electrode to a point of contact on the opposing surface defined by the toroidal member of the ground electrode.
In a third aspect of the present invention, a spark plug includes an elongated electrical insulator body defining a first bore extending longitudinally along a central axis of the body from a connector end to a firing end. A sparking electrode communicating with the first bore. The sparking electrode includes a firing tip defining a convex outer surface facing generally toward the connector end and generally having a radius of curvature. The firing tip has an outermost point generally coinciding with the central axis. A ground electrode includes a sleeve having a support portion adjacent to the firing tip of the sparking electrode. The sleeve defines a second bore accommodating at least a longitudinal end portion of the insulator body adjacent to its firing end. The ground electrode further includes a toroidal member having a convex outer surface. The toroidal member is supported by and spaced from the support portion of the sleeve such that the toroidal member is disposed slightly longitudinally inwardly from the firing tip. The toroidal member forms an annular curve disposed generally in a plane transverse to and having a radial center coinciding with the central axis of the insulator body, whereby each differential segment of the toroidal member radially thereabout is generally equidistant to the firing tip. The toroidal member is a closest portion of the ground electrode relative to the firing tip. At least a portion of the outer surface of the toroidal member opposing the firing tip has a radius of curvature of about that of the firing tip for providing a spark along a path of least resistance from the firing tip of the sparking electrode to a point of contact on the opposing surface defined by the toroidal member of the ground electrode.
One advantage of the present invention is that the spark gap between electrodes need be set only once during the manufacture of the spark plug.
Another advantage of the present invention is that the connecting members and the toroidal member cooperate to form a cage or frustoconically shaped enclosure which protects the firing tip of the sparking electrode and the insulator body from mechanical damage resulting from, for example, accidentally dropping the spark plug.
A further advantage of the present invention is that the connecting members permit the insulator body to be exposed to the atmosphere and to cleaning from the fuel/air blast created by a spark to prevent the accumulation of carbon thereon.
A further advantage of the present invention is that the spark plug provides a plurality of generally radial spark paths terminating about the surface of the toroidal member which significantly extends the operational life of the spark plug.
Another advantage of the present invention is that the firing tip of the sparking electrode protects the longitudinal end of the insulator body from damage from the fuel/air blast.